On the Dynamics of “Almost Equilibrium” Beaches in Semi-sheltered Bays Along the Southern Coast of the Gulf of Finland - The Baltic Sea Basin - page 258

decisions can be made for their protection, controlled modification (for example,
managed retreat, see Healy and Soomere 2008 ) , or reconstruction.
Another type of equilibrium exists at the mouths of large rivers such as the Narva
River where seasonal variations of the river flow and wave intensity give rise to
interesting seasonal changes of the sand bar (Laanearu et al. 2007 ) . Cyclic variations
in the height of the bar apparently are an inherent component of a specific kind of
equilibrium in such areas. A highly interesting feature of such systems is the role of
stratification of water masses in the vicinity of the sill.
The central goal of this chapter is to summarise the characteristic features of the
appearance and the dynamics of almost equilibrium beaches on the southern coast
of the Gulf of Finland and to present the recently developed applications for rapid
estimates of their basic parameters based on a few relatively easily measurable or
computable parameters. The presentation is mostly based on two examples. Pirita
Beach, located at the head of Tallinn Bay, is supported by a multitude of factors
and is a typical example of a beach whose evolution is generally slow and has been
largely controlled by development works. Narva-Jõesuu Beach in the Narva River
mouth area represents a more or less straight, widely open beach, with its highly
interesting interplay of processes forced by the littoral drift and the voluminous
river inflow.
The chapter is organised as follows. First, we describe the basic properties of
the beaches, major drivers governing the evolution of the beaches, and main fea-
tures of sediment transport. These aspects are discussed in more detail for Pirita and
Narva-Jõesuu beaches, with emphasis on estimates of the parameters of the classi-
cal (Dean's) equilibrium profile for Pirita Beach. Further on, the sediment budget
for Pirita Beach and its changes in the recent past are discussed together with the
potential of a recently developed application for express estimates of the net gain or
loss of sediment based on inversion of the Bruun Rule. Finally, the nature of sea-
sonal variations in the dynamic equilibrium caused by the interplay of littoral drift
and river discharge is analysed for Narva-Jõesuu Beach.
13.2 Forcing Factors of Sediment Transport Processes
Sediment transport processes in the littoral system are driven by a large number
of external processes such as oscillatory wave motions, wind-induced transport,
coastal currents and wave-induced longshore flows, variations of water level, sea
ice. Equally important are the local factors such as the geometry of the coast, the
sediment textural characteristics, and the availability of mobile sediments.
13.2.1 Internal Properties of Beaches
The beaches of the southern and the northern coasts of the Gulf of Finland
(Fig. 13.2 ) are completely different. The northern coast is characterised mostly by
“skären”-type beaches, the evolution of which is weakly affected by hydrodynamic